For the reliability evaluation of the ad hoc network of the UAV swarm formation, we consider the timeliness requirement of information interaction for UAV swarm formation to perform tasks, and propose a reliability evaluation scheme of the ad hoc network. Firstly, the message is analyzed. Secondly, a message transmission delay model is established using the queuing theory to calculate the time required for message transmission. Then, a message transmission reliability calculation model is established with the probability that the required time for message transmission is less than the available time as an evaluation index. Furthermore, a dynamic reliability evaluation framework is provided for UAV swarm formation to adapt to the randomness and time-varying characteristics of swarm formation system configuration and environmental changes. Finally, under different transmission task requirements, the influence of formation configuration, number of UAVs, formation scaling factor, transmission rate, network load and information interaction strength on the reliability of message transmission is simulated and analyzed. The simulation results can provide a certain reference for the formation design and the system configuration of the swarm formation.